1) Field of the Invention
The present invention relates to a single phase AC-DC converter, and particularly, relates to a single phase AC-DC converter having a construction that a PFC (Power Factor Control) power supply section, where a rectified current obtained by rectifying an electric current from an AC supply is switched, and a DC-DC power supply section, where a direct current obtained by rectifying and smoothing an electric current from an AC supply is switched, are combined together; the switching elements for switching both the sections are driven and controlled with only one servo loop.
2) Related Art
The present inventor discloses a single phase AC-DC converter where a PFC power supply section and a DC-DC power supply section are combined together in Japanese Patent Preliminarily Publication No. 11-356046. In the power supply apparatus, a PFC switching power supply section (rectified current side) having a smaller current smoothing function and a DC-DC switching power supply section (direct current side) having a greater current smoothing function are combined in a parallel manner; the rectified outputs of these sections are added together; thereby a harmonics current can be restricted, the size of the converter becomes compact, and a high efficiency can be obtained. In this apparatus, the rectified current side contributes to restrict a harmonics current, while the direct current side keeps a holding time sufficiently and reduces a ripple voltage. By making a balance of power between the rectified current side section and the direct current side section, a switching power supply apparatus is realized, which is small in size and has a high efficiency while satisfying the Class A standard for harmonics by the IEC (International Electrotechnical Commission).
In addition, so-called two-stage type AC-DC converters are also developed, which also have a PFC power supply section and a DC-DC power supply section being connected together in a cascade manner in order to restrict a harmonics current.
However, according to the AC-DC converter mentioned in Japanese Preliminarily Patent Publication 11-356046, in order to set the electric current ratio between the rectified current side section and the direct current side section so as to satisfy said standard for harmonics by IEC, it is necessary to keep the inductance at the rectified current side section considerably low. Therefore, the current waveform at the primary side of the rectified current side section becomes a narrow triangle and thus the route-mean-square current increases there. As a result, the efficiency cannot be improved as expected.
The current International Standard for harmonics current is IEC61000-3-2. According to the AC-DC converter mentioned in Japanese Preliminarily Patent Publication 11-356046, in the case that the converter is designed for accepting an input voltage in a range of 100V to 240V, the current waveform belongs to the Class A of the IEC62000-3-2, so that the converter satisfies the harmonics spectrum standard defined by the Class A without problem.
However, it is planned to change the International Standard of the EEC in future, and a provisional standard has been defined at the end of 2000. According to the provisional standard, it is required for certain appliances, i.e. personal computers, televisions, or monitors, to meet the Class D, which is stricter than the Class A. The converter according to the Japanese Preliminarily Patent Publication 11-356046 satisfies the harmonics standard in Class D if the converter is so designed as to accept an input voltage of 100xcx9c120V or an input voltage of 200xcx9c240V. However, if the converter is designed to accept an input voltage in a wider range, i.e. 100xcx9c240V, it is difficult to satisfy the harmonics standard in Class D.
On the other hand, according to the conventional two-stage type AC-DC converter, where the rectified-line side section and the direct current side section are combined together in a cascade manner, satisfies the harmonics current standard in Class D by the IEC, the efficiency, however, is poor and it is difficult to make the size of the converter compact. Further, power consumption during standby time cannot be reduced in a sufficient manner and the cost for manufacturing the converter is still high.
In order to solve the above-mentioned problems, an AC-DC converter according to the present invention comprises a PFC power supply section where a rectified current obtained by rectifying an electric current from an AC supply is switched, a DC-DC power supply section where a direct current obtained by rectifying and smoothing an electric current from an AC supply is switched, a first switching means for conducting a switching operation in said PFC power supply section, a second switching means for conducting a switching operation in said DC-DC power supply section, a drive pulse generating circuit for generating first drive pulses for driving said first switching means and second drive pulses for driving said second switching means, and a servo loop for controlling said drive pulse generating circuit; wherein said servo loop is constituted of only one serve loop; and wherein said converter comprises a duty ratio controlling means for making a duty ratio (ON time) of said drive pulses for driving said first switching means and a duty ratio (ON time) of said drive pulses for driving said second switching means different from each other in a linked manner.
In this manner, according to the AC-DC converter of the present invention, a duty ratio controlling means is provided, by which the duty ratio (ON time) of the drive pulses for driving the first switching means and the duty ratio (ON time) of the drive pulses for driving the second switching means become different from each other in a linked manner, so that efficiency is improved and the size of the converter can be made compact.
Further, the AC-DC converter according to the present invention has a characteristic in that said PFC power supply section comprises an input for connection to a source of a single phase AC supply, a first rectifying circuit for rectifying an electric current supplied from said inputs, a first transformer where one end of the primary coil thereof is connected to an output of said rectifying circuit and the other end of said primary coil is connected to said first switching means, and a first secondary side rectifying circuit for rectifying an output of the secondary side of said first transformer; said DC-DC power supply section comprises an input for connection to a source of a single phase AC supply, a second rectifying circuit for rectifying an electric current supplied from said inputs, a smoothing circuit for smoothing an output of said second rectifying circuit, a second transformer where one end of the primary coil thereof is connected to an output of said smoothing circuit and other end of said primary coil is connected to said second switching means, and a second secondary side rectifying circuit for rectifying an output of the secondary side of said second transformer; and said converter comprises an adding and smoothing circuit for adding an output of said PFC power supply section and an output of said DC-DC power supply section together and smoothing the added outputs.
According to the construction in that the PFC power supply section and the DC-DC power supply section are operated with different duty ratios and that the PFC power supply section and the DC-DC power supply section are combined in a parallel manner and the outputs of both power supply sections are added together and smoothed, the efficiency of the converter can be more improved.
Further, the AC-DC converter according to the present invention has a characteristic in that said PFC power supply section comprises an input for connection to a source of a single phase AC supply, a first rectifying circuit for rectifying an electric current supplied from said inputs, a first transformer where one end of the primary coil thereof is connected to an output of said rectifying circuit and other end of said primary coil is connected to said first switching means, and a first secondary side rectifying circuit for rectifying an output of the secondary side of said first transformer; said DC-DC power supply section comprises an input for connection to a source of a single phase AC supply, a smoothing circuit for smoothing an electric current supplied from said inputs, a second transformer where one end of the primary coil thereof is connected to an output of said smoothing circuit and other end of said primary coil is connected to said second switching means, and a second secondary side rectifying circuit for rectifying an output of the secondary side of said second transformer; and said converter comprises an output adding and smoothing circuit for adding an output of said PFC power supply section and an output of said DC-DC power supply section together and smoothing the added outputs; and wherein an inductor and a diode are inserted between said second switching means and an output of said first rectifying circuit or between said second switching means and said AC inputs.
Furthermore, the AC-DC converter according to the present invention has a characteristic in that said PFC power supply section comprises an input for connection to a source of a single phase AC supply, a first rectifying circuit for rectifying an electric current supplied from said inputs, a first transformer where one end of the primary coil thereof is connected to an output of said rectifying circuit and other end of said primary coil is connected to said first switching means, and a first secondary side rectifying circuit for rectifying an output of the secondary side of said first transformer; said DC-DC power supply section comprises an input for connection to a source of single phase AC supply, a smoothing circuit for smoothing an electric current supplied from said inputs, a second transformer where one end of the primary coil thereof is connected to an output of said smoothing circuit and the other end of said primary coil is connected to said second switching means, and a second secondary side rectifying circuit for rectifying an output of the secondary side of said second transformer; and said converter comprises an output adding and smoothing circuit for adding an output of said PFC power supply section and an output of said DC-DC power supply section together and smoothing the added outputs; wherein either said first transformer or said second transformer comprises a tertiary coil, and one end of the tertiary coil is connected to an output of said smoothing circuit and the other end thereof is connected to an output of said first rectifying circuit via a diode or to said AC inputs via a diode.
According to the construction above, harmonics which are generated in the DC-DC power supply section can be reduced, so that an AC-DC converter satisfying the strict standard in Class D by the EEC can be realized.
Moreover, the AC-DC converter according to the present invention has a characteristic in that the PFC power supply section comprises an input for connection to a source of single phase AC supply, a first rectifying circuit for rectifying an electric current supplied from said inputs, a choke coil where one end of the coil thereof is connected to an output of said rectifying circuit and the other end of the coil is connected to said first switching means; said DC-DC power supply comprises a second rectifying circuit for rectifying an output of said choke coil, a first smoothing circuit for smoothing an output of said second rectifying circuit, a transformer where one end of the primary coil thereof is connected to an output of said smoothing circuit and the other end of the primary coil is connected to said second switching means, a secondary side rectifying circuit for rectifying an output at the secondary side of said transformer, and a second smoothing circuit for smoothing an output of said secondary side rectifying circuit.
Moreover, the AC-DC converter according to the present invention has a characteristic in that the PFC power supply section comprises an input for connection to a source of a single phase AC supply, a first rectifying circuit for rectifying an electric current supplied from said inputs, a first transformer where one end of the primary coil thereof is connected to an output of said rectifying circuit and other end of the primary coil is connected to said first switching means, and a first secondary side rectifying circuit for rectifying an output at the secondary side of said first transformer; said DC-DC power supply comprises a second rectifying circuit for rectifying an output at the primary side of said first transformer, a first smoothing circuit for smoothing an output of said second rectifying circuit, a second transformer where one end of the primary coil thereof is connected to an output of said first smoothing circuit and other end of the primary coil is connected to said second switching means, a second secondary side rectifying circuit for rectifying an output at the secondary side of said second transformer, a second smoothing circuit for smoothing an output of said second secondary side rectifying circuit, and an adding and smoothing means for adding an output of said PFC power supply section and an output of said DC-DC power supply section together and smoothing the added output.
In this manner, the PFC power supply section and the DC-DC power supply section may be connected together in a cascade manner. According to the construction, a two-stage type AC-DC converter can be realized where the size is small and power consumption during standby time can be made sufficiently low.
In the AC-DC converter according to the present invention it is preferred that the drive pulses for driving the first switching means and the drive pulses for driving the second switching means turn ON at a different timing from each other but turn off at the same timing.
It is further preferred that the ON time of the drive pulses for driving the first switching means and the ON time of the drive pulses for driving the second switching means are different from each other keeping a given relation, whereby the ratio between the duty ratio of the first switching means and the duty ratio of the second switching means becomes constant.
By keeping the ratio between the duty ratio of the first switching means and the duty ratio of the second switching means constant, the AC-DC converter operates in a suitable manner without regarding the input voltage condition or the load current condition.
Furthermore, the AC-DC converter according to the present invention has a characteristic in that said drive pulse generating means comprises a drive pulse intermittently oscillation control means by which the drive pulse generating means generates the drive pulses intermittently.
By providing the drive pulses intermittently oscillation control means, the power consumption during standby time can be more reduced.
It is preferred that the drive pulses intermittently oscillation control means comprises a comparator having a hysteresis characteristic and/or a time constant so that the drive pulse output of the drive pulse generating means is controlled in accordance with the output of said comparator.
Furthermore, the AC-DC converter according to the present invention comprises a starting-up circuit for starting the drive pulse generating means up; said starting-up circuit comprises an input for connection to a source of single phase AC supply, a rectifying circuit for rectifying an electric current supplied from said inputs, a smoothing circuit for smoothing an output of said rectifying circuit, and starting-up capacitors being provided between said AC inputs and said rectifying circuits. According to the construction, an reactive current can be used to start up the drive pulse generating means and thus no starting-up resistor is required. Therefore, the power consumption there can be reduced more.
Moreover, it is preferred that the rectifying circuit is constituted of a bridge rectifying circuit, and the starting-up circuit has a voltage detecting circuit after said rectifying circuit, and a switch element, which is driven by the output of the voltage detecting circuit, being provided at an output side of either one of the starting-up capacitors.
According to the construction, when the input voltage is low, the rectifying circuit operates as a full-wave rectifying circuit, while when the input voltage is high it works as a half-wave rectifying circuit. Therefore, even if the converter is operated with a high input voltage, no current is wasted in the starting-up circuit, so that power consumption can be more reduced.
By the way, it should be noted that in this specification the DC-DC power supply section includes the rectifying circuit and the smoothing circuit at the primary side.